Treatment of inorganic hydrogels



mama' United States Patent Albert B. Schwartz, Philadelphia, Pa.,assignor to Socony Mobil Oil Company, Inc., a corporation of New York NoDrawing. Application June 26, 1952 Serial No. 295,830

6 Claims. (Cl. 252-455) This invention relates to a process forsimultaneously drying and controlling the density of inorganichydrogels.

More particularly, the present invention is directed to a method inwhich an inorganic hydrogel without prior substantial dehydration afterformation is subjected to superheated steam at an elevated pressure withthe resultant production of a gel of controlled predetermined density.

Inorganic gels are widely employed as adsorbents, cat alyst supports,and catalysts for a multitude of reactions including those ofhydrocarbon conversion. To obtain the utmost efliciency from ahydrocarbon conversion gel catalyst, it is necessary to adjust thecatalyst density to a predetermined value which will depend in part uponthe conditions under which the conversion operations are carried out.Generally, the catalyst is contacted with hydrocarbon vapors atconversion conditions, for example, 800 F. to 1000 'F. atatmospheric orgreater pressures. The reaction which takes place is essentially acracking to produce lighter hydrocarbons, but is accompanied by a numberof complex side reactions, such as aromatization, polymerization,alkylation, and the like. As a result of these complex reactions, acarbonaceous deposit is laid down on the catalyst which is commonlycalled coke. The coke tends to seriously impair the catalytic efiiciencyof the catalyst for the principal reaction and the conversion reactionis therefore suspended after coke, to the extent of a few percent byweight, has accumulated on the catalyst. The catalytic surface is thenregenerated by burning the coke in a stream of oxidizing gas and thecatalyst is returned to the conversion stage of the cycle. The rate atwhich coke can be burned from the spent catalyst decreases with anincrease in the density of the catalyst. The activity and hardness ofthe catalyst are also affected by its density, the hardness of thecatalyst increasing with an increase in density. It is, accordingly,desirable to adjust the density of the gel catalyst to an intermediatevalue between the maximum and minimum limits of density control in orderto obtain the most beneficial elfects of activity, hardness, andregeneration properties in the resulting catalyst.

It has heretofore been known that the density of certain gel catalystscan be effected by subjecting the hydrogel to a hydrothermal treatmentwhich comprises contacting the freshly formed hydrogel with hot waterfor a specified period of time. The duration of the contact time and thetemperature of the water used under such conditions determines thedensity of the dried gel. This method of density control has thedisadvantage of being time-consuming under ordinary conditions ofoperation. Thus, in order to adjust the apparent density of a freshlyformed hydrogel to between 0.60 and 0.75 gram per cc. using water at 100F., approximately 36 to 48 hours are required. While this time oftreatment may be reduced by increasing the temperature of the water,such procedure is not always feasible since subsequent airdrying ofhydrogels which have undergone treatment "ice with excessively hot waterleads to considerable gel breakage. Such breakage is especiallyundesirable where the production of gel particles of substantiallyuniform size and shape is sought, for example in the manufac ture ofspheroidal bead-like gel particles. The method of density control usinghot water is further not effective in treatment of hydrogels containingappreciable amounts of magnesia or chromia, i.e., hydrogels containingmore than about 3 percent by weight on a dry basis of these metaloxides. Thus, while silica and silica-alumina hydrogels upon treatmentwith hot water undergo reduction in apparent density, hydrogels ofmagnesia or chromia or hydrogels containing an appreciable amount ofmagnesia or chromia in combination with other metal oxides or silica forsome unknown reason are substantially unaifected by treatment with hotwater in so far as control of density is concerned.

Drying of inorganic hydrogels either after adjustment of density withhot water or in the absence of such adjustment has been accomplished bypassing warm air over the hydrogel or by contacting the hydrogel withsuperheated steam at substantial atmospheric pressure. The extent ofdrying will depend somewhat on the use which it is desired to make ofthe product but, in any event, the drying is carried to a stage beyondthat at which maximum shrinkage of the gel is obtained. In the usualoperation, further drying proceeds after syneresis or shrinkage has beenvirtually completed until the gel is substantially dry; that is, the gelpossesses open pores free of liquid although it still contains arelatively small percentage of water which may be removed by drying atrelatively high temperatures.

It is an object of the present invention to provide a process in whichdensity control and drying of inorganic hydrogels may be carried onsimultaneously. Obviously, drying of hydrogels cannot be eliected whilethe same are in contact with hot water under the usual conditions foradjustment of density. A further object of the invention is theprovision of a comparatively rapid method for drying inorganic hydrogelswith concurrent control of the density. A still further object is toprovide a prowhich has not undergone substantial dehydration afterformation, with superheated steam at an elevated pressure in excess of100 pounds per square inch and maintaining said pressure until shrinkageof the hydrogel is substantially complete. In a preferred embodiment ofthe invention, a hydrogel, which has not undergone substantialdehydration atter formation, is dried to a predetermined density bybringing the same into contact with superheated steam at a pressure inthe range of 100 to 500 pounds per square inch, the choice of pressurebeing correlated with the desired density of the gel product. Thehydrogel undergoing treatment, in accordance with the instant method,may be freshly formed or may have been previously aged, base-exchanged,impregnated, or otherwise treated providing that no substantialdehydration of the hydrogel occurs after formation.

superheated steam, that is, steam at a temperature so that it possessesmore than enough heat to maintain its existence as a dry gas at thegiven pressure, is necessarily employed as the predominant dryingmedium. Slight dilution of the steam may be tolerated within bounds ofthe preferred embodiments of the invention. However, the drying gasshould be predominantly steam, i.e., at least about percent or morewater vapor by voluume,

fusion rates of the gases.

The temperature of the superheated steam is necessarily above saturationtemperature at the pressure employed. Usually, the temperature of thesuperheated steam will be between about 350 F. and about 800 F. It iscontemplated that the process described herein is applicable for dryingand controlling the density of inorganic hydro gels generally withoutregard to composition or physical form. The method has, however, beenfound to be particularly useful in drying uniformly shaped hydrogelparticles such as beads. In such instance, bed depth of hydrogelparticles up to 12 inches may be conveniently treated with superheatedsteam at a pressure above 100 pounds per square inch. The method,further, has been found to be particularly useful in treating hydrogelscontaining appreciable amounts of magnesia or chromia with theproduction of gels of predetermined density.

The desired density of the final gel catalyst will depend on thecoke-burning capacity of the regenerating kiln employed, the particulardegree of hardness desired in the catalyst and the activity of theresulting catalyst. High density catalysts have the disadvantages ofregenerating very slowly and giving excessive deposits of coke duringthe hydrocarbon conversion cycle. Low density catalysts are very fragileand are sometimes relatively inactive. Taking these factors intoconsideration, generally a gel having particle density of between about1 and 1.4 gram per cc. will be employed. The apparent density of the gelwill generally be between 0.65 and 0.9 gram per cc.

Particle density, as used herein, is the density of the gel particlesincluding the pores and is measured on the dried and calcined particles.Apparent density, on the other hand, includes also the free spacebetween the gel particles and is therefore affected by the size, shapeand packing of the particles.

Thus, hydrogels which normally lead to gels of high density when driedat atmospheric pressure and low temperature may, in accordance with theinstant process, be dried in super-heated steam at elevated pressure andtemperature. The higher the drying temperature and pressure, the loweris the density of the finished gel. Since the drying rate of the gel isdependent upon the amount of superheat in the steam and the steam ratethrough the bed of gel, the drying rate at a given temperature can becontrolled by adjusting the steam pressure and steam rate. The minimumdrying time is that suflicient to attain substantially completeshrinkage of the hydrogel. For a gel processed under given conditions,the greater the percentage of metal oxide in the gel, the higher is thedensity of the finished catalyst. Usually, a drying time consistent withthe pressure and temperature conditions of the superheated steam dryingmedium employed will be in the range of /3 to 8 hours. Drying times upto 24 hours may in some instances be used particularly where a deep beddepth of hydrogel particles are being dried.

Studies of the various gels of dilfering composition have establishedthat within the foregoing ranges of pressure and temperature of thesuperheated steam drying medium,

different gels respond differently to the specified drying conditions.Thus, chromia-alumina gels of approximately 10-40 percent by weight Cr Oand 60-90 percent by' weight A1 normally contain pores of very smalldiameter, thereby limiting the transfer of hydrocarbon vapors andregeneration gases through the gel pores to the dif- Upon dryingchromia-alumina hydrogels having the above-indicated composition rangeon a dry basis with superheated steam at pressures in excess of about100 pounds per square inch, the resultant gels exhibit improvedregeneration characteristics. One of the principal shortcomings ofsilica-magnesia gel catalyst containing 20 to 40 percent by weight MgOand 60 to 80 percent by weight SiO is due to the small porous structureof the gel. Because of such small porous structure, excessive amounts ofcoke are produced during cracking of petroleum hydrocarbons employingthis catalyst and also extremely long times are required forregeneration. in accordance with the method of the invention,silica-magnesia gels containing 20 to 40 percent MgO andsilica-alumina-magnesia gels containing 10 to 30 percent metal oxides,said gels having large porous structure and reduced apparent density canbe prepared by drying the corresponding hydrogels in superheated steamunder controlled conditions of high pressure and temperature. In thecase of silica-alumina and silica gels, the hot water treatment which isfrequently employed to lower the density of the gel may be eliminatedwith the drying pressure and temperature of superheated steam adjustedto give a finished gel of the desired density.

Having described in a general way the nature of this invention, it maybe more readily understood by reference to the following illustrativenon-limiting examples:

Example 1 V A silica-magnesia hydrosol was prepared by mixing threeseparate reagent streams comprising magnesia, sodium silicate, andsulfuric acid in a mixing nozzle. The magnesia stream was composed of 13pounds of light magnesia slurred in 181 pounds of water. The sodiumsilicate stream was composed of 105 pounds of sodium silicate solution,having an Na O/SiO ratio of 1:322 and .a gravity of 41 B., and 105pounds of Water. The sulfuric acid stream was composed of 17.4 pounds of96.3% sulfuric acid and 127 pounds of water. The three streams weremixed under the following conditions:

cc./min.

Acid solution rate 265 Silicate solution rate 400 Magnesia suspensionrate 335 The resulting hydrosol was allowed to flow over a dividing coneinto an oil medium wherein the hydrosol in the form of globules set tospheroidal particles of hydrogel. The time of gelation of theabove-prepared hydrosol was 4.9 seconds at F. The resulting hydrogel hada pH of 9.3. The hydrogel particles, so formed, were treated for 6 hoursat F. while covered with water, after which the hydrogel particles werebaseexchanged with a magnesium sulfate solution, washed free of solublesalts and dried under the conditions described below.

Portions of the above silica-magnesia hydrogel were dried in superheatedsteam under varying conditions of pressure and temperature. Theresulting gel composites in each instance were calcined for 3 hours at1300" F. in air and tested as hydrocarbon conversion catalysts inaccordance with the Cat-A method described in National Petroleum News,volume 36, page R-537, August 2, 1944.

The gel contained about 25% by weight MgO and about 75% by Weight SiOThe drying conditions, physical properties of the resultant gel, andCat-A activity results together with regeneration characteristics ineach instance (55 are set forth below:

Drying Conditions Physical Properties Oat-A Activity Regenen. 4 ationPress, Steam Apparent Particle Surface Pore Avg. Pore Gasoline, Coke,Gas, Gas Gasoline Gasoline Index p.s.i.g Temp., Density, Density, Area,Volume, Diameter, Percent Percent Percent Gravity W F. g./cc. gJcc.MJ/g. cc lg A. Volume Weight Weight Example 2 V A silica-magnesiahydrosol was prepared by mixing three separate reagent streams havingthe compositions described in Example 1. The three streams were mixed inthis instance under thefollowing conditions:

. .CcJmin Acid solution rate V V 265 Silicate solution rate 400 Magnesiasuspension'rate 500 The resulting hydrosol was allowed to flow over adividing cone into an oil medium wherein the hydrosol in the form ofglobules;set to spheroidal particles of hydrogel. The time of gelationof the above-prepared hydrosol was 3.6 seconds at 91 F. The resultinghydrogel particles having a pH of 10.2 were processed as in Example land dried under conditions described below.

Portions of the above silica-magnesia hydrogel were dried in superheatedsteam under varying conditions of pressure and temperature. Theresulting gel composites in each instance were calcined for 3 hours at1300? F. in air and tested as hydrocarbon conversion catalysts inaccordance with the Cat-A method The gel contained about 37.1% by WeightMgO and about 62.9% by weight to remove this amount of catalyst depositwas a direct measure of the rate of carbon burn-off. The rate of carbonburn-01f was compared with the rates from two standard catalysts, one ofwhich (a silica-alumina bead catalyst having a bulk density of 1.0) wasassigned an arbitrary regeneration index of zero and the other (anactivated clay), 'a regeneration index. of 100. The regeneration indexis then defined as follows:

Time for zero standard-time for unknown R1 t T1me for zero standard timefor 100 standard Example 3 A silica-alurnina-magneSia hydrosol Wasprepared by I taining aluminum sulfate in a mixing nozzle. The mag- 7three streams were mixed under the following conditions:

S10 The drying conditions, physical properties of the .Cc./min.resultant gel, and Cat-A activity resultstogether with Acid-aluminumsulfate solution rate 265 regeneration characteristics in each .instanceare set forth Silicate solution rate 400 below: Magnesia suspension rate310 Drying Conditions Physical Properties Oat-A Activity r .RegenerationPress, Steam Apparent Particle Surface Pore Avg. Pore Gasoline, Coke,Gas, Gasoline Gasoline Index p.s.i.g Temp, Density, Dens 37, Area,.Volume, Diameter, Percent Percent Percent Gas Coke Gas F. g./cc. g./cc.M. 2/g. cc./g. A. Volume Weight Weight Gravity 280 1.08 1.74 366 I 0.18120. 52.1 8.3 9.0 1.66 6.3 5 s 37 484 0.84 1.38 490 0.358 29. 46.7 6.67.4 I 1.51 7.1 6 3 51 547 0.72 1. 21 467 0 464 40 45.2 4. 7 6.1 1.48 9.6 7 4 69 From the results of Examples 1 and 2, it'will be seen that adistinct improvement in gasoline-to-coke and gasoline-to-gas ratios areachieved with silica-magnesia gel catalysts which have been dried insuperheated steam at pressures of about 100 to 500 pounds per squareinch as compared to atmospheric pressure drying and, further, that animprovement in the regeneration characteristics of silica-magnesia gelcatalysts is obtained. as indicated by the increase in regenerationindex of the catalyst resulting from high pressure drying in superheatedsteam. The operation of the regenerability test employed was as follows:

Fifty cc. (packed volume) of the catalyst were placed in an electricallyheated glass tube. The standard cracking stock (pressed distillate froma parafiinic-mixed base crude; A.P.I. gravity of 30.5; boiling rangeof600-700" F.) was vaporized and passed through the catalyst bed at 900Rand at a liquid hourly space rate of 0.6 until a carbonaceous depositof22i2 grams per liter of catalyst was laid down. After purging thevapors from the system, the temperature of the catalyst was raised tol000:5 F. and air was passed through the bed at a rate of 600cc.(measured at room conditions) per minute. The regeneration was carriedout at this rate until 85 The resulting hydrosol was allowed to flowover a dividing cone into an oil medium wherein the hydrosol in the formof globules set to spheroidal particles of hydrogel. The time ofgelation of the above-prepared hydrosol was 4.7 seconds at 86 Theresulting hydrogel particles had a pH- of 9.8. The hydrogel particles,so formed, were treated for 6 hours at 160 F. while covered with water,after which the hydrogel particles were base-exchanged with an aluminumsulfate solution, washed free of. soluble salts and dried under thecondi tions shown below.

Portions of theabove silica-alumina-magnesia hydrogel were dried insuperheated steam under varying conditions of-pressure, and temperature;The resulting gel composites in' each instance were calcined for hoursat 1300" F. in air and tested as hydrocarbon conversion catalysts inaccordance with-the Cat-A method. The

gel contained 14.4% by weight A1 0 4.7% by weight percent of the depositwas'burned off. The time required instance are set forth below:

Drying Conditions Oat-A Activity Physical Property, Regenw I 1 Apparenteration Press qS team Density, (liasolinte, PColre,t 1 Gas, t G[GastGasoline Gasoline Index .s. .g emp. g. cc. ercen ercen ercen ravi p Y F.Wt Wt. y Gas 7 m le 4 A silicaaalumina-chromia hydrosol was prepared bymixing a sodium silicate solution containing by weight 14.0% SiO 4.4% NaO, 81.6% H and an acidic solution containing by weight 3.83% A1 (SO0.13%

the hydrogel particles were base-exchanged with aluminum sulfatesolution, washed free of soluble salts and dried under the conditionsshown below.

Portions of the above silica-alumina-chromia hydrogel were dried insuperheated steam under varying conditions of pressure and temperature.The resulting gel composites in each instance were calcined for 5 hoursat 1300 F. in air and tested as hydrocarbon conversion catalysts inaccordance with the Cat-A method. The gel contained about by weight A1 00.15% by weight Cr O with the remainder being S102. The dryingconditions, apparent density of the resultant gel, and Cat-A activityresults together with regeneration characteristics are set forth below:

From the data embodiedin the foregoing examples, it will be seen that areduction in apparent density is obtained by drying hydrogels of varyingcomposition in superheated steam at elevatedpressures in excess of 100pounds per square 'inch up to'about 500 pounds per square inch. It willfurther be noted that the density decreases with increase in pressureand temperature of the superheated steam drying medium and that thedensity of theresultant gel may accordingly be adjusted to apredetermined value by control of the pressure and temperatureconditions maintained during drying.

I claim: 1 p

1. A method for producing an inorganic oxide gel characterized by aparticle density of between about 1 and 1.4 grams per cubic centimeter,which comprises forming an inorganic oxide hydrogel which, if dried andcalcined at atmospheric pressure, would have a particle density inexcess of 1.5, subjecting said hydrogel, without prior substantialdehydration thereof, to contact with superheated steam at a temperaturebetween about 350 F. and about 800 F. and a pressure between 100 and 500pounds per square inch until shrinkage of the hydrogel is substantiallycomplete, and thereafter calcining the resultant dried, shrunkenhydrogel at an elevated tem- F perature of at least 1025 F.

2. A method for producing an inorganic oxide gel characterized by aparticle density of between about 1 Drying Conditions Cat-A ActivityPhysical Property, Regen- Apparent oration Press, TSteam Density,Gasoline, l Cclre, PGas, GGast Gasoline Gasoline Index p.s.i.g emp. g.cc. Percent ercent ercent, ravi y F. v01. wz. Wt

Example 5 and about 1.4 grams per cubic centimeter, which com- Achromia-alurnina hydrosol was prepared by mixing a chromic acetatesolution containing 11.1 grams Cr O per 100 cc. and having a chromic toacetate ion ratio of 1:3 with a sodium aluminate solution containing.26.6 grams A1 0 per 100 cc. and having, a sodium to aluminum ion ratioof 1.3. The above solutions were mixed in a maxing nozzle under thefollowing conditions:

The resulting hydrosol was introduced into an oily medium in the form ofglobules which set in 7 seconds at 121 F. and a pH of 11.7 to spheroidalparticles of chromia-alumina hydrogel. The particles were thereaftertreated with a 20% by weight aqueous solution of (NI- Q 80 for 24 hours,washed free of soluble salts and dried under conditions described below.

Portions of the above chromia-alumina hydrogel were dried in superheatedsteam under varying conditions .of pressure and temperature. The driedgel was calcined 3 hours at 1025 F. in a steam atmosphere. The gelcontained approximately 32% by weight Cr O and 68% by Weight A1 0 Thedrying conditions and physical properties of the resultant gel in eachinstance are set forth below:

Drying Physical Properties Conditions Steam Particle Apparent SurfacePore Avg. Press, Temp., Density, Density, ea, Volume, Pore p.s.i.g. F.g./cc. g./ce. MJ/g. cc./g. Diameter, A.

239 1. so 0. 96 240 0.34s 58 I 5110... 570 1. 22 O. 78 271 0. 549 81prises forming an inorganic oxide hydrogel which, if dried and calcinedat atmospheric pressure, would have a particle density in excess of 1.5,subjecting said hydrogel, without prior substantial dehydration thereof,to contact with superheated steam at a pressure in the range of 100 to500 pounds per square inch and a temperature above the saturationtemperature for a period of between A and 8 hours until shrinkage of thehydrogel is substantially complete, and thereafter calcining theresultant dried, shrunken hydrogel at substantially atmospheric pressureand an elevated temperature of at least 1025" F.

3. A method for producing a gel consisting essentially of a majorproportion of silica and a minor proportion of alumina andcharacterizedby a particle density of between about 1 and about 1.4grams per'cubiccentimeter, which comprises forming a hydrogel having asolids content consisting essentially of a major proportion of silicaand a minor proportion of alumina and which, if dried and calcined atatmospheric pressure, would have a particle density inexcess of 1.5,subjecting said hydrogel, without prior substantial dehydration thereof,to contact with superheated steam at a temperature between about 350 P.and about 800 F. and a pressure between 100 and 500 pounds per squareinch until shrinkage of the hydrogel is substantially complete, andthereafter calcining the resultant dried, shrunken hydrogel at anelevated temperature of atileast 1025 F.

-4. A method for producing a chromina-alurnina gel having'a content of10 to 40 percent by weight of chromia forming a chromia-alumina hydrogelwhich, if dried and calcined at atmospheric pressure, would have aparticle density in excess of 1.5, subjecting said hydrogel, withoutprior substantial dehydration thereof, to contact with superheated steamat a temperature between about 350 F. and about 800 F. and a pressurebetween 100 and 500 pounds per square inch until shrinkage of thehydrogel is substantially complete, and thereafter calcining theresultant dried, shrunken hydrogel at an elevated temperature of atleast 1025 F.

5. A method for producing a silica-magnesia gel having a content of topercent by weight of magnesia and to percent by weight of silica andcharacterized by a particle density of between about 1 and about 1.4grams per cubic centimeter, which comprises forming a silica-magnesiahydrogel which, if dried and calcined at atmospheric pressure, wouldhave a particle density in excess of 1.5, subjecting said hydrogel,without prior substantial dehydration thereof, to contact withsuperheated steam at a temperature between about 350 F. and about 800 F.and a pressure between and 500 pounds per square inch until shrinkage ofthe hydrogel is substantially complete, and thereafter calcining theresultant dried, shrunken hydrogel at an elevated temperature of atleast 1025 F.

6. A method for producing a silica-alumina-magnesia gel having a contentof 10 to 30 percent by weight metal oxides and remainder, silica, andcharacterized by a particle density of between about 1 and about 1.4grams per cubic centimeter, which comprises forming asilicaalumina-magnesia hydrogel which, if dried and calcined atatmospheric pressure, would have a particle density in excess of 1.5,subjecting said hydrogel, without prior substantial dehydration thereof,to contact with superheated steam .at a temperature between about 350 F.and about 800 F. and a pressure between 100 and 500 pounds per squareinch until shrinkage of the hydrogel is substantially complete, andthereafter calcining the resultant dried, shrunken hydrogel at anelevated temperature of at least 1025 F.

References Cited in the file of this patent UNITED STATES PATENTS1,762,228 Holmes June'lO, 1930 1,772,055 Miller et a1. Aug. 5, 19302,358,202 Behrman Sept. 12, 1944 2,377,547 Fuchs June 5, 1945 2,378,155Newsome et al June 12, 1945 2,477,664 'Shabaker July 29, 1947 2,694,673Kimberlin et al Nov. 16, 1954 2,698,305 Plank et a1. Dec 28, 19 54

1. A METHOD FOR PRODUCING AN INORGANIC OXIDE GEL CHARATERIZED BY APARTICLE DENSITY OF BETWEEN ABOUT 1 AND 1.4 GRAMS PER CUBIC CENTIMETER,WHICH COMPRISES FORMING AN INORGANIC OXIDE HYDROGEL WHICH IF DRIED ANDCALCINED AT ATMOSPHERIC PRESSURE, WOULD HAVE A PARTICLE DENSITY INEXCESS OF 1.5, SUBJECTING SAID HYDROGEL, WITH OUT PRIOR SUBSTANTIALDEHYDRATION THEREOF, TO CONTACT WITH SUPERHEATED STEAM AT A TEMPERATUREBETWEEN ABOUT 350* F. AND ABOUT 800*F. AND A PRESSURE BETWEEN 100 AND500 POUNDS PER SQUARE INCH UNTIL SHRINKAGE OF THE HYDROGEL ISSUBSTANTIALLY COMPLETE, AND THEREAFTER CALCINING THE RESULTANT DRIED,SHUNKEN HYDROGEL AT AN ELEVATED TEMPERATURE OF AT LEAST 1025*F.